Abstract:

Even when a membrane sheet contains an inorganic material, the membrane
sheet and a support plate are properly deposited by a laser emission. In
a manufacturing method of a flat membrane element lapping a membrane
sheet performing solid-liquid separation on a support plate supporting
the membrane sheet and emitting a laser to a mutual joint portion to
deposit the membrane sheet and the support plate, when the membrane sheet
contains an inorganic material, the support plate is formed by a material
having laser penetration and the laser is emitted from the support plate
side to the joint portion.

Claims:

1. A flat membrane element comprising:a support plate formed by a material
having laser penetration;a first membrane sheet of which circumferential
portion is deposited onto a first surface of the support plate; anda
second membrane sheet formed to have a larger size than the first
membrane sheet and arranged on a second surface of the support plate so
that the second membrane sheet is deposited at an outer peripheral side
of a deposition line of the first membrane sheet.

Description:

[0001]This is a Divisional of application Ser. No. 11/640,317 filed Dec.
18, 2006. The entire disclosure of the prior application is hereby
incorporated by reference.

[0005]A flat membrane element of this kind is set in water to be processed
in a dipped manner and used to filtrate the water to be processed. FIG. 5
is a partial sectional view showing a general structure of a flat
membrane element. A support plate 1 is formed such that a circumferential
edge 2 thereof has a flame shape and a water passing portion 3 is formed
in the inner portion thereof. A membrane sheet 4 is formed on both the
face of the support plate 1. A suction port 5 is connected with a
circumferential edge 2. In addition, the outer surface of the
circumferential edge 2 and the membrane sheet 4 has a joint portion 6
formed by lapping each other. By effecting negative pressure in the
suction port 5 or by effecting positive pressure from the outer surface
of the membrane sheet 4, the water to be processed is filtrated and the
filtrated water transmitted through the membrane sheet 4 is discharged
from the suction port 5 via the water passing portion 3. Note that the
water passing portion 3 of the support plate 1 is specially treated to
have a figure through which the filtrated water can pass freely while
supporting the surface of the membrane sheet 4 to prevent the membrane
sheet 4 attached from sagging.

[0006]The membrane sheet 4 is called for example an ultrafiltration
membrane or an ultrafilter membrane, and that made of synthetic resin is
used in general. Also, the support plate 1 made of synthetic resin, which
shows a favorable jointing characteristic with the membrane sheet 4, is
used. It is important for the flat membrane element to ensure
watertightness of the joint portion 6, so that a method of jointing the
support plate 1 and the membrane sheet 4 with an adhesive is widely
employed. However, the method of using the adhesive easily causes
deviation in adhesive force in addition to the problems that the adhesive
easily deteriorates to lower the watertightness and that leak from the
lateral direction along the joint surface of the membrane sheet 4 is
easily caused.

[0007]As a method of improving the problem in the jointing method using
the adhesive, a flat-membrane-element manufacturing method in which a
membrane sheet is deposited on a support plate by lapping the membrane
sheet and the support plate each other and emitting a laser to the
mutually jointed portion is disclosed in Japanese Patent Application
Laid-Open No. 2005-279580. In this method, the membrane sheet is made of
a material having larger laser penetration and the support plate is made
of a material having larger laser absorption property, in which the
membrane sheet is deposited on the support plate by emitting a laser from
the membrane sheet side to the joint portion while pressing the membrane
sheet toward the support plate. In the method disclosed in Japanese
Patent Application Laid-Open No. 2005-279580, the flat membrane element
having strong adhesive force at the joint portion in which the
deterioration and the leak from the lateral direction of the membrane
sheet are hard to be caused can be manufactured at relatively low costs.

[0008]However, some flat membrane elements contain an inorganic material
such as ceramics or metal fine particles as a membrane sheet. In the flat
membrane elements as described above, even when the laser is emitted from
the membrane sheet side, the laser does not penetrate due to the
inorganic material interrupting it. Therefore, it is impossible to
deposit the joint portion of the membrane sheet and the support plate,
indicating a problem that the method disclosed in Japanese Patent
Application Laid-Open No. 2005-279580 is not applicable thereto.

SUMMARY OF THE INVENTION

[0009]An object of the present invention is to provide a manufacturing
method of a flat membrane element capable of depositing a joint portion
of a membrane sheet and a support plate by a laser emission even when the
membrane sheet contains an inorganic material by bringing a solution to a
problem in a conventional art as described before.

[0010]In order to attain the above-described object, a manufacturing
method of a flat membrane element according to the present invention is a
manufacturing method of a flat membrane element, in which a membrane
sheet performing solid-liquid separation and a support plate supporting
the membrane sheet are lapped each other while the support plate is
formed by a material having laser penetration, and the membrane sheet and
the support plate are deposited by a laser emission from the support
plate side to the joint portion. In the above-described method, the joint
portion lapping the membrane sheet onto the support plate is pressed by a
pressing member formed by a material having laser penetration and the
laser is emitted from an outside of the pressing member to the joint
portion. Further, the membrane sheet includes a skin layer, a support
layer and a wetting layer therebetween, and the laser is emitted so that
the support layer side is directly deposited onto the support plate by
jointing the support layer side with the support plate. The joint potion
is allowed to include a deposition agent having laser absorption property
therein. This is effective when the membrane sheet is made of an
inorganic material. Further, when the flat membrane element has a
structure in which the membrane sheet is attached onto both surfaces of
the support plate, it is preferable that a first membrane sheet is
deposited onto one surface of the support plate and, after that, a second
membrane sheet to be attached onto the other surface of the support plate
is arranged such that the joint portion thereof with the support plate
comes outside the edge portion of the first membrane sheet to be
deposited.

[0011]According to the present invention, the support plate is formed by
the material having laser penetration and the laser is emitted from the
support plate side to the joint potion, so that the joint portion of the
membrane sheet and the support plate can be deposited easily by the laser
emission even when the membrane sheet contains the inorganic material and
without laser penetration.

[0012]Further, when the deposition agent having laser absorption property
is intervened in the joint portion, it is possible to choose an optimal
deposition agent having higher laser absorption property separately from
the material composing the membrane sheet, so that the manufacturing of
the flat membrane element with high reliability can be realized.
Therefore, the present invention is applicable even when the membrane
sheet is formed by the inorganic material only.

[0013]Further, when the second membrane sheet to be attached onto the
other surface of the support plate is arranged so that the joint potion
thereof with the support portion comes outside the edge portion of the
first membrane sheet to be deposited on the other surface, after the
first membrane sheet is deposited onto the one surface of the support
plate, the present invention can be properly embodied even when the flat
membrane element has the structure in which the membrane sheet is
attached onto both the surfaces of the support plate, respectively.

[0014]Furthermore, according to the present invention, a flat membrane
element including: a support plate formed by a material having laser
penetration; a first membrane sheet of which circumference is attached to
the one surface of the support plate; and a second membrane sheet to be
arranged on the other surface of the support plate, which is formed to
have a larger size as compared with the first sheet and deposited on the
outer peripheral side of the deposition line of the first membrane sheet,
is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a partial sectional view showing a first embodiment of a
manufacturing method of a flat membrane element according to the present
invention;

[0016]FIG. 2 is a partial front view showing a part of a commercialized
flat membrane element by cutting a part thereof;

[0017]FIG. 3 is a partial sectional view showing a second embodiment of
the manufacturing method of the flat membrane element according to the
present invention;

[0018]FIGS. 4(1) to 4(3) are partial sectional views showing a third
embodiment of the manufacturing method of the flat membrane element
according to the present invention; and

[0019]FIG. 5 is a partial sectional view showing a general structure of a
flat membrane element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]FIG. 1 is a partial sectional view showing a first embodiment of a
manufacturing method of a flat membrane element according to the present
invention. A membrane sheet 10 is roughly composed of a skin layer 10a, a
wetting layer 10b and a support layer 10c. The skin layer 10a bears a
solid-liquid separating part and is formed by an inorganic material such
as ceramics or metal fine particles. The support layer 10c bears a part
of supporting the entire membrane sheet 10 and is formed by, for example,
a synthetic resin such as polyethylene. It is also effective to mix a
pigment such as carbon black into the synthetic resin by which laser
absorption property increases. The wetting layer 10b is formed in the
wetted state in a manner that the material composing the skin layer 10a
is entered into, the support layer 10c. These respective layers actually
do not have clear border lines as shown in the drawing, and the wetting
layer 10b has the inorganic material composing the skin layer 10a at high
ratio on the skin layer 10a side and the ratio reduces as it comes closer
to the support layer 10c side.

[0021]A support plate 20 is composed of a circumferential edge 20a of a
frame shape and a water passing portion 20b in the frame portion. The
water passing portion 20b is specially treated to have a figure through
which the filtrated water can pass freely while supporting the surface of
the film sheet 10 to prevent the film sheet 10 attached from sagging. The
support plate 20 is formed by a material having laser penetration,
preferably, by a synthetic resin with high transparency. The synthetic
resin mixed with the pigment has lower transparency in which the laser
penetration lowers, being not desirable as a material for the support
plate 20.

[0022]When manufacturing the flat membrane element by depositing the
membrane sheet 10 and the support plate 20, the under surface of the
support plate 20 is lapped onto the upper surface of the membrane sheet
10 having the support layer 10c on its upper side, as shown in FIG. 1.
Subsequently, the joint portion at which the membrane sheet 10 and the
support plate 20 are lapped is pressed from the upper surface of the
circumferential edge 20a of the support plate 20 by a pressing member 26
to increase adhesiveness of the membrane sheet 10 and the support plate
20 at the joint portion. Subsequently, a laser 24 is emitted from the
upper surface side of the support plate 20 to the joint portion by a
laser designator 22.

[0023]The laser 24 reached to the circumferential edge 20a penetrates the
circumferential edge 20a having the laser penetration to reach the upper
surface of the support layer 10c of the membrane sheet 10. Since the
support layer 10c is formed by the synthetic resin having high laser
penetration as described before, the laser 24 reached to the support
layer 10c is absorbed by the support layer 10c to fuse the resin of the
support layer 10c by heat of mixing at this time. The heat of mixing is
conveyed further to the wetting layer 10b of the membrane sheet 10 to
fuse the resin of the wetting layer 10b as well, so that fusion zone can
be enlarged further to the skin layer 10a. Further, the fusion heat of
the resin of the support layer 10c is conveyed to the under surface of
the circumferential edge 20a of the support plate 20 to fuse the resin
composing the circumferential edge 20a.

[0024]By performing the fusing operation of the synthetic resin based on
the emission of the laser 24 as descried above along the path of
deposition, the fusion zone cured by natural cooling after the laser
emission forms a weld 28. The weld 28 deposits the membrane sheet 10 and
the support plate 20 tightly and, at the same time, the deposition zone
reaches further to the skin layer 10a, so that the transverse section of
the wetting layer 10b of the membrane sheet 10 is shielded. Accordingly,
the leak in the lateral direction arising from the wetting layer 10b or
the support layer 10c in the membrane sheet 10 is effectively prevented.

[0025]Note that the pressing member 26 is preferably formed by a material
having high laser penetration as in the support plate 20. Specifically,
the pressing member 26 is frequently arranged at a position interfering
with the laser emission of the laser 24, however, the pressing member 26
formed by the material having high laser penetration allows the emission
of the laser 24 to be performed via the pressing member 26, so that the
workability in the fusing operation performed along the path of
deposition is dramatically improved.

[0026]FIG. 2 is a partial front view showing a part of a commercialized
flat membrane element by cutting a part thereof. The membrane sheet 10 is
deposited onto the support plate 20 by the weld 28 formed at all the
circumferential edge 20a. The circumferential edge 20a is provided with a
suction port 30 to suck the filtrated water, and the water permeated
through the membrane sheet 10 goes through the water passing portion 20b
and is discharged outside from the suction port 30. FIG. 2 shows the case
where the membrane sheet 10 and the support plate 20 are deposited by the
single band of weld 28, however, when two bands of weld portions are used
to deposit the membrane sheet 10 and the support plate 20, a flat
membrane element with further rigidity can be manufactured, as described
in Japanese Patent Application Laid-Open No. 2005-279580.

[0027]FIG. 3 is a partial sectional view showing a second embodiment of
the manufacturing method of the flat membrane element according to the
present invention. In FIG. 3, the elements denoted by the same numerical
references as in FIG. 1 are the same elements as in the first embodiment
and therefore their detailed descriptions will be omitted here. In the
present embodiment, a deposition agent 34 having laser absorption
property intervenes into the joint portion of a membrane sheet 32 and the
support plate 20. The deposition agent 34 can exist in an intervening
manner as shown in the drawing by applying the deposition agent 34 onto
the joint portion of the upper surface of the membrane sheet 32 or the
joint portion of the under surface of the support plate 20 in advance and
by lapping them. Further, when the deposition agent 34 is formed not by a
material of an applicable type but a type capable of keeping its shape,
the deposition agent 34 is formed in accordance with the path of
deposition and placed on the upper surface of the joint portion of the
membrane sheet 32 and, after that, the support plate 20 is lapped
thereon, so that the deposition agent 34 can intervene to be put in the
state as shown in the drawing. In the present embodiment, with the
emission of the laser 24, the deposition agent 34 absorbs the laser to
fuse at first, and the fusion heat is conveyed to the membrane sheet 32
and the circumferential edge 20a of the support plate 20 to promote the
deposition. According to the method of the present embodiment, it is
possible to select the optimal deposition agent 34 having high laser
absorption property separately from the material composition of the
membrane sheet 32, so that the manufacturing of the flat membrane element
with high reliability can be realized. Accordingly, the present method is
also applicable to the case where the membrane sheet 32 is composed of
the inorganic material only. However, the inorganic material generally
has a high fusing point being difficult to fuse by the laser emission.
Therefore, when the membrane sheet 32 is composed of the inorganic
material only, it is important to select and/or determine the deposition
agent 34 and/or the laser emission conditions so that the fused substance
of the deposition agent 34 enters deeply into between the particles of
the inorganic material to form the layer like the wetting layer 10b
described in the first embodiment.

[0028]FIGS. 4(1) to 4(3) are partial sectional views showing a third
embodiment of the manufacturing method of the flat membrane element
according to the present invention. In FIGS. 4(1) to 4(3), the elements
denoted by the same numerical references as in FIG. 1 are the same
elements as in the first embodiment and therefore their detailed
descriptions will be omitted here. Generally, the flat membrane element
adopts the structure in which the membrane sheet is attached onto both
the surfaces of the support plate, respectively, as shown in FIG. 5. When
manufacturing the flat membrane element of the structure as described
above, the method shown in FIGS. 4(1) to 4(3) is adopted.

[0029]Specifically, in the first step, a first membrane sheet 36 is
deposited onto one surface of the support plate 20 by emitting the laser
24 as shown in FIG. 4 (1). In the second step, as a second membrane sheet
38 to be attached onto the other surface of the support plate 20, that
having sufficiently larger plane area than that of the first membrane
sheet 36 is prepared in advance. Next, as shown in FIG. 4 (2), the
support plate 20 having the first membrane sheet 36 deposited in the
first step is reversed to be arranged such that the joint portion of the
second membrane sheet 38 and the support plate 20 comes outside the edge
of the first membrane sheet 36 and the second membrane sheet 38 is
deposited by emitting the laser 24. As a result, as shown in FIG. 4 (3),
a flat membrane element 40, in which the first membrane sheet 36 is
attached onto the one surface of the support plate 20 and the second
membrane sheet 38 having sufficiently larger plane area than that of the
first membrane sheet 36 is attached onto the other surface of the support
plate 20, is manufactured.

[0030]According to the present embodiment, after the first membrane sheet
36 is deposited onto the one surface of the support plate 20, the second
membrane sheet 38 to be attached onto the other surface of the support
plate 20 is arranged so that the joint potion thereof with the support
plate 20 comes outside the edge portion of the first membrane sheet 36 to
be deposited, so that the method of emitting the laser 24 from the
support plate 20 side can be properly performed even when the flat
membrane element 40 is structured to have the first and second membrane
sheets 36, 38 attached on both the surface of the laser designator 22,
respectively.

[0031]As has been described, in the present invention, the support plate
composing the flat membrane element is formed by the transparent material
having laser penetration, and the laser is emitted in a penetrating
manner from the support plate side to the membrane sheet to be deposited
to the support plate while at least the portion of the membrane sheet to
be deposited is pressed by the pressing member from the support plate
side, so that the membrane sheet is deposited thereto. When the support
layer to be the joint portion of the deposition and formed by the resin
of the membrane sheet is made to have the laser absorption property by
being impregnated the pigment such as carbon black, the joint by
deposition is further ensured. When the joint is performed to set the
deposition agent, which is made to have the laser absorption property by
being impregnated the pigment such as carbon black, into the joint
portion in an intervening manner and the laser is emitted to the
deposition agent such that the laser penetrates the support plate, the
membrane sheet can be jointed surely. Ideally, such portions of the
support plate and the pressing member that the laser penetrates are made
transparent, and the support layer and/or the deposition layer of the
membrane element to be jointed side is made black.